The present invention relates to electric meters containing electronic demand registers and, more particularly, to physical construction of electronic demand registers adapted for ease of assembly and efficient integration with their electric meters.
Conventional electric meters employ an aluminum disk driven as a rotor of a small induction motor by an electric field at a speed which is proportional to the electric power being consumed by a load. Geared dials, or cyclometer discs, integrate the disk motion to indicate the total energy consumed, conventionally measured in kilowatt hours (one kilowatt hour equals one thousand watts of power consumption for one hour).
In addition to the above measurement of consumption, some electric meters contain means for separating the consumption into those parts of consumption occurring during predetermined peak and off-peak hours and for recording maximum demand during a predetermined period of time in order to adjust billing according to such parameters. In one such demand meter disclosed in U.S. Pat. No. 3,586,974, a mechanical demand register records the power usage during a predetermined period of time and stores the value for later reading. The predetermined period of time may be, for example, the time between meter readings, or a period of time corresponding to the billing period of the utility providing the power. A clockwork mechanism restarts the demand register at the ends of regular demand intervals of, for example, a fraction of an hour, so that, at the end of the predetermined period, the stored value represents the highest value of power usage occurring during any one of the regular demand intervals in the predetermined period.
Mechanical demand registers, such as disclosed in the above U.S. Patent, have limited flexibility. The design of a particular meter physical configuration is not transferable to another meter having a different physical configuration. In addition, the demand-measurement functions of a particular demand register cannot be redefined without major mechanical redesign. Greater flexibility may be obtained using electronic acquisition, integration and processing of power usage. An electronic processor such as, for example, a microprocessor, may be employed to manage the acquisition, storage, processing and display of the usage and demand data. U.S. Pat. Nos. 4,179,654; 4,197,582; 4,229,795; 4,283,772; 4,301,508; 4,361,872 and 4,368,519, among others, illustrate the flexibility that electronic processing brings to the power and energy usage measurement. Each of these electronic measurement devices includes means for producing an electronic signal having a characteristic such as, for example, a frequency or a pulse repetition rate, which is related to the rate of power usage. The electronic processor is substituted for the mechanical demand register of the prior art to keep track of the power usage during defined periods of time.
Various aspects of an electronic demand register which may benefit from the packaging technique of the present invention are disclosed in U.S. patent applications Ser. Nos. 599,684, U.S. Pat. Nos. 4,571,692; 599,685, 4,627,000; 599,736, 4,591,782; 599,744, 4,625,163; 599,683, 4,573,141; 599,735, 4,598,248; 599,743, 4,594,545; 599,742, 4,620,150 all filed on Apr. 12, 1984 and Ser. Nos. 550,407, now abandoned; 550,142, now abandoned both filed on Nov. 10, 1983 the disclosures of which are herein incorporated by reference. For present purposes, it is sufficient to state that one desirable characteristic of an electronic demand register should be ease of manufacture using snap-together assembly techniques. In addition, since the electronic demand register is called on to perform many functions, it necessarily requires the inclusion of a large number of parts when compared to the number of parts in the electro-mechanical portion of the electric meter. As a consequence, it can be anticipated that an electronic demand register of an electric meter may require field service more often than the remainder of the electric meter. Thus, a second important desirable characteristic of an electronic demand register is ease of troubleshooting and service.
The mechanical kilowatthour register of an electric meter must accommodate a plurality of different voltages and loads. The line voltage available for driving the aluminum disk of a particular installation is accommodated by a suitable choice of a voltage coil in the electric meter. Different loads are accommodated by selecting a desired relationship between disk rotation and mechanical dial readings through the use of scaling by mechanical gearing. In this way, a single basic electro-mechanical design of an electric meter is adaptable to a large number of installation-specific applications.
It is desirable to provide an improved electronic demand register having corresponding, or greater, universality of use in installation-specific situations. Such universality is achieved in the referenced demand register through the use of programmed constants which perform scaling corresponding to that performed by mechanical gearing, and perform other functions for adapting a universal electronic demand register design to a particular installation. The programmed constants reside in the volatile memory of a digital processor during normal operation and are transferred to an on-board, non-volatile memory upon the occurrence of a real or apparent power outage, as well as upon a limited number of other types of occurrences. Removal of the electronic demand register from the electric meter is recognized as an apparent power outage triggering the non-volatile storage of the programmed constants. In addition, existing billing data is also stored in the non-volatile memory.
A favored technique for field service on an electronic demand register includes substitution of a known-good demand register for one that is apparently in a failed condition. In order to avoid the need to reprogram the programmed constants for a particular application, and to avoid losing stored billing data, a method was disclosed in the referenced patent applications for copying the contents of a non-volatile storage in one electronic demand register to a non-volatile storage in another electronic demand register which may then be substituted for the original electronic demand register. It is desirable that the package for an electronic demand register provide a suitable interface for a programmer which is capable of reading the contents of a non-volatile storage in an electronic demand register which is to be replaced and for writing the thus-acquired data into a non-volatile storage in a replacement electronic demand register.
In order to reduce the cost of an electronic demand register, it is desirable to eliminate the need for a transformer therein to adapt the electronic demand register to the voltage existing in the installation. A convenient way of eliminating a transformer includes employing dropping resistors of an appropriate resistance to reduce the line voltage to a desired standard value. Such dropping resistors are disclosed in the referenced patent applications. When dropping resistors are substituted for transformers, additional precautions are desirable to avoid accidental contact between people and conductive materials in the electronic demand register.